The use of the conventional electromechanical bell ringer has been the primary signaling device used in telephones for a great number of years. In recent years, however, tone ringers considered to be more desirable have been replacing the electromechanical bell ringer due to advances in electronic technology. The tone ringers provide a signal generally considered substantially more pleasing to the average ear than the jangle of an electromechanical bell ringer. Also, space requirements through use of tone ringers are minimized. These tone ringers comprise electronic circuitry that responds to conventional low frequency power ringing signals on a telephone line, and also a tone generating transducer that provides an alerting signal to a telephone subscriber. An example of such a tone ringer is disclosed in U.S. Pat. No. 3,740,490, issued to R. F. McAlonie et al., on June 19, 1973.
Telephone ringers have to operate over a loop whose length can vary considerably. Although more efficient than electromechanical bell ringers, tone ringers of the prior art are optimized to operate over loops not exceeding a certain length since the ringers have an operational voltage range. Telephone extensions with ringers increase the load presented to the ringing voltage resulting in a further decrease in the available voltage. Thus, the value of the current available to the tone ringer is a critical, sensitive factor, particularly so in those instances where multiple sets are terminated on a line. It is desirable, therefore, to provide a tone ringer which allows for efficient operation over a wide range of loop lengths and multiple extensions being terminated on the telephone line.